The Perrin 02-07 WRX & STI rotated mount turbocharger kit is one of the most comprehensive and best designed on the market. The Perrin rotated mount turbo kit utilizes redesigned exhaust and intake plumbing to install a large Garrett turbocharger on your WRX or STI, without being limited by the stock under-the-manifold turbo inlet and internal wastegate. Perrin's rotated turbo placement allows for straight, unobstructed intake plumbing and fitment of even the biggest turbochargers.

The Perrin turbo kit either requires a Perrin front-mount intercooler with blow-through MAF tube, or some form of engine management that eliminates the MAF sensor. This kit makes no provisions for the stock MAF sensor.
Engine management, fuel system upgrades, and supporting modifications are required with this kit.
2005 STI models and all 5-speed models require some grinding of the transmission housing for clearance and a soft bend in the dip-stick sleeve for clearance.
Building the engine internals is highly recommended for when installing these kits.
As with all turbo kits, there is some "tweaking" / "elbow grease" required for installation - i.e. trimming, unbolting, minor grinding, etc.